Microfluidic surface processing device and method

ABSTRACT

The present invention is notably directed to a microfluidic surface processing device including a microfluidic probe head with at least one aperture, on a face, including at least an outlet aperture; and a surface processing structure extending outward and perpendicular with respect to the face, the processing structure being further dimensioned and located with respect to the outlet aperture such that it can intercept a flowpath of liquid dispensed via the outlet aperture. The present invention is further directed to related apparatuses and methods.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/928,604, filed Jun. 27, 2013, which claims priority under 35 U.S.C.§119 from Patent Application No. GB1211557.2 filed Jun. 29, 2012, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to the field of microfluidic surfaceprocessing devices as well as related methods.

2. Description of Related Art

Microfluidics generally refers to microfabricated devices, which areused for pumping, sampling, mixing, analyzing and dosing liquids.Prominent features thereof originate from the peculiar behavior thatliquids exhibit at the micrometer length scale. Flow of liquids inmicrofluidics is typically laminar. Volumes well below one nanoliter canbe reached by fabricating structures with lateral dimensions in themicrometer range. Reactions that are limited at large scales (bydiffusion of reactants) can be accelerated. Finally, parallel streams ofliquids can be accurately and reproducibly controlled, allowing forchemical reactions and gradients to be made at liquid/liquid andliquid/solid interfaces. Microfluidics is accordingly used for variousapplications in life sciences.

For example, inkjets were designed to deliver ink in a non-contact modebut not in the presence of a liquid. Other techniques can furtherpattern surfaces at higher resolution but are limited in their abilityto operate in a liquid environment. Liquid environments minimize dryingartifacts, denaturation of biomolecules, and enable working withbiological specimens as cells or tissues.

For patterning surfaces and analyzing samples on a surface in thepresence of a liquid environment, several strategies were developed toovercome limitations of closed microfluidics. Some strategies rely onconfining liquids near a surface or, still, delivering a precise amountof biomolecules in a well defined region of a liquid. Scanningnanopipettes and hollow probes (resembling probes used in Atomic ForceMicroscopy) were also developed for patterning biomolecules on surfaceswith micrometer accuracy.

As another example, a non-contact microfluidic probe technology (or“MFP”) was developed (see e.g. US 2005/0247673), which allows to patternsurfaces by adding or removing biomolecules, create surface densitygradients of proteins deposited on surfaces, localize reactions atliquid interphases in proximity to a surface, stain and remove adherentcells on a surface, amongst other applications.

In another technical field, scanning probe microscopy (or SPM) was bornwith the invention of the scanning tunneling and the atomic forcemicroscope. In brief, it aims at forming images of sample surfaces usinga physical probe. Scanning probe microscopy techniques rely on scanningsuch a probe, e.g. a sharp tip, just above or in contact with a samplesurface whilst monitoring interaction between the probe and the surface.An image of the sample surface can thereby be obtained. Typically, araster scan of the sample is carried out and the probe-surfaceinteraction is recorded as a function of position. Data are thustypically obtained as a two-dimensional grid of data points. Theresolution achieved varies with the underlying technique: atomicresolution can be achieved in some cases. Typically, eitherpiezoelectric actuators or electrostatic actuation are used to executeprecise motions of the probe.

Two main types of SPM are the scanning tunneling microscopy (STM) andthe atomic force microscopy (AFM). The invention of STM was quicklyfollowed by the development of a family of other similar techniques(including AFM), which together with STM form the SPM techniques.Incidentally, the “probe” or “probe tip” used in SPM techniques shouldbe distinguished from the “probe” as meant in MFP; the two types ofprobes differ functionally, structurally and dimensionally from eachother.

Amongst SPM techniques, thermal probe-based techniques are known, whichoperate in air but are not suitable for operation in liquids. Theyfurther are limited to thermal activation of existing functional unitsat the processed surface. Among AFM techniques, one may for examplecite:

-   -   “Applications of dip-pen nanolithography” (K. Salaita et al.        Nature Nanotech., 2007, 2, 145-155); and    -   “Nanofountain-Probe-Based High-Resolution Patterning and        Single-Cell Injection of Functionalized Nanodiamonds” (Loh, O.,        et al., Small, 2009. 5: pp 1667-1674).

Dip-pen is operating in air and generates drying artifacts. TheNanofountain probe is operating in liquid. It can basically be regardedas a micro-scale pipette. The processing liquid can diffuse away fromthe point of interest and can contaminate the surrounding liquid. Thus,it can be realized that with the above techniques, in situ operation inbuffer solutions with sub-micrometer precision, is not possible. Thereis accordingly a need for high resolution surface processing devicesthat can easily be operated in a liquid environment.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a microfluidic surface processingdevice, including: a microfluidic probe head having, on a face, at leastone aperture, including at least an outlet aperture; and a processingstructure extending outward and perpendicular with respect to the face,the processing structure being dimensioned and located with respect tothe outlet aperture such that it can intercept a flowpath of liquiddispensed via the outlet aperture.

Another aspect of the present invention provides a method of surfaceprocessing, including: providing a microfluidic surface processingdevice, the processing structure positioned facing a surface to beprocessed; dispensing a processing liquid via the outlet aperture,whereby the processing structure intercepts a flowpath of the processingliquid dispensed; transferring particles in the liquid to the surfacevia the processing structure, by bringing the processing structure incontact with the surface, wherein a surface of the processing structureis functionalized to enable transport of the particles to an apex of theprocessing structure; and bringing the processing structure out ofcontact with the surface to create a pattern thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a 3D view of a simplified representation of a microfluidicsurface processing device, according to embodiments.

FIG. 2 is another 3D view of the device of FIG. 1, in operation: thedevice comprises a probe tip that intercepts a flowpath of liquiddispensed via an outlet aperture and collected via an inlet aperture,according to embodiments.

FIGS. 3-4.B illustrate variants to FIG. 1.

FIGS. 5-6 are respectively a front view and a side view (simplifiedrepresentation) of the device of FIG. 1.

FIG. 7 is a side view (simplified representation) of a variant to FIGS.1 and 5 device where a rounded processing structure is used instead of aprobe tip, according to embodiments.

FIGS. 8-13 are side views of variants to the device of FIG. 1, whichinclude a cantilever with one free portion that can be urged against anoutlet orifice. The devices of FIGS. 10-11 further include an electricalcircuit to measure an electrical response, e.g. conductivity, electricalcapacitance, electrochemical potential in an inlet conduit and feedbackcontrol means, as in embodiments.

FIG. 14 illustrates a step of a method of surface processing, where aprobe tip continuously inked by a processing liquid is brought incontact with a surface to be processed, according to embodiments.

FIGS. 15-19 each illustrate a similar step, but according to otherembodiments:

In FIG. 15 the processing liquid is further confined in an immersionliquid. Particles of the liquid are transferred to the surface via aprobe tip;

In FIG. 16 a lipid bilayer is generated at a surface of the processingstructure (a probe tip);

In FIG. 17 molecular species are further transported via such a lipidbilayer;

In FIG. 18 the probe tip is energized to enable catalysis or a chemicalreaction to take place at the processed surface; and

In FIG. 19 a rounded processing structure is used instead of a probetip, as in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A simple idea underlying the present invention is to adjoin a surfaceprocessing structure such as a SPM-like probe tip to a microfluidicprobe head (or MFP head), conveniently located with respect to liquidoutlet/inlet apertures of the MFP head, such that in situ operation inbuffer solutions becomes possible. The processing structure need not becompletely wetted by the processing solution delivered by the MFP:molecules move/diffuse along the processing structure, such that SPMlike patterning resolution can be achieved without contamination of thesurrounding area.

According to first aspect, the present invention is embodied as amicrofluidic surface processing device, including: a microfluidic probehead having, on a face thereof, at least one aperture, this including atleast an outlet aperture; and a processing structure extending outwardand perpendicular with respect to the face, the processing structurebeing further dimensioned and located with respect to the outletaperture such that it can intercept a flowpath of liquid dispensed viathe outlet aperture, in operation.

In embodiments, the microfluidic probe head further includes at least aninlet aperture on the face, wherein: the outlet aperture and the inletaperture are dimensioned and positioned such as to allow for collecting,via the inlet aperture, liquid dispensed via the outlet aperture; andthe processing structure is dimensioned and located with respect to theinlet aperture and the outlet aperture to intercept a flowpath of liquiddispensed via the outlet aperture and collected via the inlet aperture,in operation.

In variants, the microfluidic surface processing device furtherincludes: an electrical circuit configured to measure an electricalresponse, such as, e.g. an electrical conductivity, an electricalcapacitance or an electrochemical potential, of liquid collected via theinlet aperture; and, preferably, feedback control means coupled to theelectrical circuit, preferably configured to control a rate ofprocessing liquid dispensed via the outlet aperture based on anelectrical response measured via the electrical circuit, in operation.Such a feedback control means could also be used to determine thedistance between the device and the surface. Also, combinations ofdifferent types of electrical responses could be measuredsimultaneously, if needed.

Preferably, an average diameter of the outlet aperture at the level ofthe face is between 0.5 and 1000 micrometers; a distance between theprocessing structure and the outlet aperture is between 5 and 2000micrometers; and, preferably, a distance between the outlet aperture andan inlet aperture of the microfluidic probe head, if any, is between 5and 2000 micrometers.

According to embodiments, the device further includes a cantilevermechanically connected to the head, and wherein the processing structureis a probe tip, the latter terminating the cantilever.

Preferably, the cantilever is a scanning probe microscope cantilever,and wherein preferably, the cantilever is anchored to the head, and morepreferably is anchored at one point only to the head. The cantilever isfor example an AFM cantilever. It can for instance also be mounted tosome other holder, at least partly independent from the MFP head.

In preferred embodiments the cantilever is fixed via a fixed portion atthe face, the fixed portion distant from the probe tip, and thecantilever further includes a free portion, the latter extendingopposite to the probe tip with respect to a main axis of the cantileverand configured to seal one of the apertures when urged against it.

In embodiments, the fixed portion is opposite to the probe tip withrespect to the free portion; or the free portion is opposite to theprobe tip with respect to the fixed portion.

According to another aspect, the invention is embodied as a method ofsurface processing, including: providing the device of any one of theabove embodiments, with the processing structure facing a surface to beprocessed; dispensing a processing liquid via the outlet aperture,whereby the processing structure intercepts a flowpath of the processingliquid dispensed; and transferring particles in the liquid to thesurface via the processing structure, by bringing the processingstructure in contact with the surface, and wherein, preferably, asurface of the processing structure is functionalized to enabletransport of the particles to an apex of the processing structure. Theparticles can be as small as molecules. The processing liquid does notneed to get in contact with the surface, such that resolution can beenhanced.

Preferably, the processing structure is further brought out of contactwith the surface to create a pattern thereon.

In embodiments, the microfluidic probe head of the device providedfurther includes an inlet aperture on the face, the outlet aperture andthe inlet aperture dimensioned and positioned such as to allow forcollecting via the inlet aperture liquid dispensed via the outletaperture, and the processing structure is located to intercept aflowpath of liquid dispensed via the outlet aperture and collected viathe inlet aperture, the method further including: collecting via theinlet aperture processing liquid dispensed via the outlet aperture.

An immersion liquid can further be provided between the face and thesurface, the processing liquid dispensed within the immersion liquid,and preferably such as to form a laminar flow of processing liquidconfined in the immersion liquid.

Preferably, the method further includes measuring an electricalconductivity of liquid collected via the inlet aperture, and,preferably, the method further includes controlling a rate of processingliquid dispensed via the outlet aperture based on the measuredelectrical conductivity.

According to embodiments, transferring particles further includes:generating a lipid bilayer at a surface of the processing structure;and, preferably, transferring particles further includes transportingmolecular species via the lipid bilayer to transfer the molecularspecies to the surface. Note that, more generally, a “conveyor beltsystem” can be used instead of a lipid bilayer.

Preferably, the device provided further includes a cantilevermechanically connected to the head, and the processing structure is aprobe tip terminating the cantilever, and transferring particles furtherincludes energizing the processing structure, preferably thermally orelectrically, to enable a chemical reaction to take place at thesurface. The reaction could also be a catalytic reaction with e.g.platinum or other metals.

In preferred embodiments, the cantilever of the device provided is fixedvia a fixed portion at the face, the fixed portion distant from theprobe tip, and the cantilever further includes a free portion, thelatter extending opposite to the probe tip with respect to a main axisof the cantilever and configured to seal the outlet aperture when urgedagainst it, and dispensing further includes adjusting a rate ofprocessing liquid toward the free portion to pivot or deflect theportion and let liquid flow though the outlet aperture.

Aspects of the present invention can be embodied as an apparatus or as amethod. Configuration and processing of preferred embodiments of thepresent invention with reference to the accompanying drawings aredescribed herein below wherein identical objects are denoted by the samereference numeral in all of the drawings unless otherwise specified. Itshould be understood that embodiments that follow are intended todescribe preferred aspects of the invention without limiting the scopethereof.

Main aspects of the invention are now generally described in referenceto FIGS. 1 to 19. Each of these figures depicts a microfluidic surfaceprocessing device 10 a-10 h or a portion thereof. In each case, thedevice includes a MFP head 16, which exhibits at least one outletaperture 11 on a face 17 of the MFP head 16. Typically, the face 17 isthe surface processing face, i.e., meant to face the surface 40 to beprocessed. However, other configurations can be contemplated, as seen inFIG. 4.A. The microfludic surface processing device 10 a-10 h furtherincludes a processing structure 21, 21 a, 22. The processing structure21, 21 a, 22 is preferably a SPM-like probe terminated by a probe tip21, as in e.g., FIGS. 1, 2, 4-6. It can otherwise be embodied as arounded structure (see e.g., FIG. 7), or still a protruding, tip-shapedstructure (FIG. 3). Other suitable shapes and dimensions can becontemplated. In all cases, this processing structure 21, 21 a, 22 mustextend outward and perpendicular with respect to one face 17 of the MFPhead 16. This means, strictly speaking, that a projection of thisprocessing structure 21, 21 a, 22 onto an axis perpendicular to the face17 differs from zero. The processing structure 21, 21 a, 22 isfurthermore dimensioned and located with respect to the outlet aperture11 such that it can intercept a flowpath (e.g., laminar) of liquid 15dispensed via the outlet aperture, in operation. Thus, the projection ofthe processing structure 21, 21 a, 22 onto an axis perpendicular to face17 must be substantially larger than zero, in order for the processingstructure 21, 21 a, 22 to be able to intercept the delivered flowpath ofliquid 15, in operation.

Such a device markedly simplifies surface nano-processing under liquid.In operation, this device is provided close to a surface 40 to beprocessed, and oriented such that the processing structure 21, 21 afaces the surface 40. Then, a processing liquid 15 is dispensed via theoutlet aperture 11, see e.g., FIG. 2, 5 or 6; the processing structure21, 21 a intercepts the flowpath of the liquid 15 dispensed. Particles151, 153, 155 in the liquid 15 can thus be easily guided to the surface40 via the processing structure 21, 21 a, by bringing the processingstructure 21, 21 a in contact with the surface 40. Bringing theprocessing structure 21, 21 a in and out of contact with the surface 40allows for creating specific patterns, as illustrated in FIGS. 15-19.The latter steps are repeated as needed to create involved patterns onthe surface 40, a thing that advantageously finds a number ofapplications.

Preferably, the MFP head 16 further includes at least one inlet aperture12 on the face, as depicted in FIGS. 1-4.A. The outlet aperture 11 andsaid inlet aperture 12 are dimensioned and positioned such as to allowfor collecting via the inlet aperture 12, liquid 15 dispensed via theoutlet aperture 11, typically in a laminar regime (as known per se). Theprocessing structure 21, 21 a is located between the inlet aperture 12and the outlet aperture 11 and dimensioned so as to intercept theflowpath of liquid 15 dispensed via aperture 11 and collected viaaperture 12, in operation. In operation, liquid 15 dispensed at theoutlet aperture 11 is (at least partly) collected via the inlet aperture12. The inlet 12 and outlet 13 apertures can otherwise be defined asorifices terminating respective conduits/channels, adequately arrangedin the MFP head 16 and beyond to suitable dispense and aspirate liquid15, with the help of pumps and/or any adequate mechanism. MFP heads 16equipped with inlet 12/outlet 11 apertures, conduits, pumps, etc., areknown per se.

A better control of particle deposition is achieved when using acombination of outlet 11/inlet 12 apertures as particles 151, 153, 155to be transferred to the surface 40 remain confined in the liquid 15 (asmall volume of processing solution can be dispensed by the MFP head 16,as illustrated in FIG. 2. More generally, a well defined volume ofprocessing solution can be provided by the MFP head 16. A processingstructure 21, 21 a such as a probe tip 21 of an AFM-like cantilever canthus be positioned in the liquid 15 envelope and be continuously inkedwith chemicals present in the liquid 15. The chemicals shall forinstance diffuse along the processing structure 21, 21 a e.g., towardsthe apex of the AFM probe 20, and accordingly be deposited onto thesubstrate surface 40. Proper surface functionalization of the processingstructure 21, 21 a can be realized, if necessary, to ensure efficienttransport of the chemicals to the apex of the structure.

In practice, the average diameter of the outlet aperture 11 (and of theinlet aperture 12 if any) at the level of the face 17 is typicallybetween 0.5 and 1000 micrometers. The outlet aperture 11 shouldpreferably be small enough to achieve a local confinement, e.g.,slightly larger than the probe tip 21. Such a confinement of e.g., 150micrometers can be achieved with outlet apertures 11 of about 20 to 50micrometers. It can however be smaller, e.g., 0.5 micrometers can easilybe fabricated. The inlet aperture 12 is in some cases much larger,especially where one seeks to prevent from clogging by particles/dust.This strongly depends on the application sought. The apertures 11, 12end, each, a respective outlet/inlet conduit having preferably the samediameter as the corresponding aperture. Yet, the sizes of the inlet 12and outlet 11 can substantially differ, e.g., “small” outlet, “large”inlet. The flow characteristics enabled by such dimensions are typicallysuited for a range of applications as contemplated therein. In addition,the distance between the processing structure 21, 21 a and the outletaperture 11 is preferably set between 5 and 2000 micrometers. Thisdistance shall notably depend on the working distance, deflection anddimensions of the processing structure 21, 21 a, e.g., an AFMcantilever. A MFP can easily provide a flow confinement of 500micrometer thickness. If the AFM is to far away, it looses contact fromthe confinement. The processing structure 21, 21 a is typically“between” the inlet 12 and outlet 11 apertures (i.e., its projectiononto face 17 is typically in the middle of the apertures, althoughslight offset can be contemplated. Thus, a distance between the outletaperture 11 and the inlet aperture 12 is typically more than 5micrometers, but also less than 2000 micrometers. With such dimensions,a stable confinement can be achieved. Smaller dimensions are impracticalin terms of fabrication, while larger dimensions can result in anunstable confinement. As said earlier, laminar flows of liquid 15 arepreferably contemplated.

The preferred materials are typically the ones used formicroelectromechanical systems (MEMS), Silicon, glass, ceramics,polymers, metal coatings and chemical surface functionalization.Depending on the application, materials should be biocompatible and/orresistant against the solvents/solutions used. The flow rates wouldpreferably be between 0.01 to 100 microliters per minute.

As touched above, the processing structure 21, 21 a is preferably shapedand dimensioned as a probe tip 21, as depicted in FIGS. 1-4.B. Themicrofludic surface processing device 10 a-10 h can furthermore includea cantilever 22, mechanically connected to the MFP head 16, e.g.,protruding perpendicularly or extending parallel to a face 17 thereof,e.g., the processing face 17. The probe tip 21 terminates the cantilever22 in that case, like in SPM probes in general, as depicted in FIGS. 1,2, 4.A-B. Such embodiments combine the resolution capabilitiesachievable with probe tips 21 together with flexible liquid 15 handlingof MFP heads 16.

Note that in the cases of FIG. 3, the processing structure 21 isprovided directly on the face 17, i.e., protruding from the face 17,whereas in the embodiments of FIGS. 1, 2, 4.A-B, the probe tip 21terminates a cantilever 22. Yet, in FIGS. 1, 2, the probe 20 (21-23) isindirectly connected to the MFP head 16, via a fixed point 23. In FIGS.4.A-B, the cantilever 22 protrudes directly from an end face of the MFPhead 16. Owing to the orientation of the tip 21 in 4.A-B, the processingface 17 remains parallel to the average plane of the MFP head 16 shownand the processing face 17 differs from the face which exhibitsapertures 11, 12. The device 10 c 2 of FIG. 4.B includes only one outletaperture 12 (no inlet aperture 11), as required in a minimalconfiguration of a microfludic surface processing device 10 a-10 haccording to embodiments. The structures of FIGS. 4.A-B offer greaterphysical protection for the probe 21, 22 but can be more difficult tofabricate than the devices of FIGS. 1-3.

In this respect, the portions of the devices 10 c 1 and 10 c 2 of FIGS.4.A-B can be manufactured single-piece, or not, using usual fabricationtechniques known in the field of MFPs. Instead, the devices of FIGS. 1,2 can benefit from fabrication techniques known from the both the fieldsof MFP and SPM: the MFP head 16 can use typical MFP fabricationtechniques, while the probe tip 21 and cantilever 22 can be fabricatedusing any suitable SPM fabrication techniques. The cantilever 22 can forinstance be anchored at one or more points 23 to the MFP head 16, e.g.,to a part or a surface 16 b contiguous with a mesa 16 a, which includesthe apertures 11, 12, and this, using techniques known from SPM devicefabrication. Note that the mesa 16 a, although helpful for setting thedistance between the MFP apertures 11, 12 and the probe tip 21 toprovide proper liquid-tip interaction, is however not essential; it canfor instance be omitted, as depicted in FIGS. 5-13. In fact, thenecessity of a mesa 16 a depends on the mounting geometry of the SPM tothe MFP head 16.

The scope of this invention is nevertheless not limited to devices usingSPM-like probe tips. For the transfer purpose, e.g., a local dispensingof the reactants, any geometrical guiding structure 21 a, e.g., arounded or tip-shaped structure that protrudes from the face 17 can beused, as depicted in FIG. 3, 7 or 19. Of course, the processingstructure 21 a needs be appropriately dimensioned and located withrespect to apertures 11, 12 and a resulting liquid 15 flow. Flow ratescould be between 0.01 and 100 microliters per minute. The volumesconfined (excluding volumes in the tubing and the head) are typicallybetween 200 picoliters and 1 microliter.

Devices such as represented in FIG. 7 or 19 can additionally include areservoir 20 a in fluid communication with the surface 40 of theprocessing structure 21 a, for example to suitably functionalize thissurface 40 with respect to chemicals contained in the liquid 15, as tobe discussed later.

Referring back to FIGS. 1-2, here the SPM probe 20 is anchored at onepoint 23 to the MFP head 16. The other way round, the MFP head 16 can bemounted on a whole SPM apparatus (not shown), with the MFP head 16mounted integral with the SPM probe tip 21. Thus present embodimentsextend to SPM apparatuses equipped with a MFP head 16, suitably arrangedwith respect to the probe tip 21. Such apparatuses benefit from accurateSPM positioning means (not shown), which can advantageously be used inapplications contemplated herein. Examples shall be described later inreference to FIGS. 14-19.

Referring to FIGS. 8 to 13, in embodiments, the probe 20 b is fixed tothe MFP head 16 via a fixed portion 23, 23 a, on the same side as theside of face 17 including the apertures 11, 12. The fixed portion isdistant from the probe tip 21. The probe 20 b further includes a freeportion 24, 24 a, which extends opposite to the probe tip 21 withrespect to the main axis (i.e., the average direction) of the cantilever22. In other words, the free portion 24, 24 a protrudes toward the MFPhead's 16 processing face 17, while the probe tip 21 protrudes towardthe surface 40 to be processed, in operation. As further seen in FIG.8-13, the free portion 24, 24 a (and more generally the cantilever 22)can be configured such as to seal one of the apertures 11, 12 (typicallythe outlet aperture 11) when urged against it. Accordingly, various waysof flow control mechanisms can be simply enabled as discussed below.

Different cases might be envisaged. A first case concerns the “normally”open valve, i.e., open by default, as depicted in FIG. 8. Here the fixedportion 23 is opposite to the probe tip 21 with respect to the freeportion 24. Owing to the cantilever 22 configuration obtained, if theprobe tip 21 touches the surface 40 (FIG. 9), the force acting on theprobe tip 21 pushes on the supporting cantilever 22, and in turn bringsthe free portion 24 in contact with the outlet aperture 11. Thismechanism allows for controlling the flow of processing liquid 15dispensed via the MFP head 16.

A second case is that of the “normally” closed valve, as depicted inFIGS. 12-13. Here the free portion 24 a is opposite to the probe tip 21with respect to the fixed portion 23 a. When the probe tip 21 touchesthe surface 40 (FIG. 13), the cantilever 22 pivots, which brings thefree portion 24 out of contact with the outlet aperture 11, such thatprocessing liquid 15 can be released.

The MFP head 16 can include a number of additional features, designed toappropriately dispense and collect the liquid 15. This can for instancebe one or more reservoirs (not shown), fluid channels and circuitry (notshown), pumps, (not shown), electrical circuits, etc., as known in theart of MFP.

Next, referring to FIGS. 10-11, in embodiments, the microfluidic surfaceprocessing device 10 f-10 g can further include an electrical circuit70, 70 a, the latter configured to measure an electrical conductivity ofliquid 15 collected via the inlet aperture 12. The measure is typicallycarried out at the level of a conduit (or channel) above the inletaperture 12. This can be used to monitor the quantity of liquid 15collected via the inlet aperture 12.

This further provides a means for sensing the delivery of the processingliquid 15. In that respect, this circuit 70, 70 a can furthermore becoupled to feedback control means 72, 72 a. The later can for instancecommand a valve (not shown) to control a rate of liquid 15 dispensed viathe outlet aperture 11, based on the electrical response, e.g.conductivity, electrical capacitance, electrochemical potential measuredvia the electrical circuit 70, 70 a, in operation. In the circuit 70,conductivity is measured between the immersion liquid and the aspiratedliquid in the channel. Circuit 70 a measures the composition of theliquid 15 directly in the channel. Both circuits give insight into thecomposition of the liquid 15. From this the valve position as well asthe gap height can be determined. So they can be used for distance orfluid control. Thus, measuring an electrical response in the aspirationconduit provides a means for sensing the delivery of the processingliquid 15, which can be combined with a valve control mechanism. Thismakes it in turn possible to sense the probe tip 21—sample interaction.

Another aspect of the invention concerns methods of surface processing.Examples of such methods shall now be described in reference to FIGS. 14to 19. As already explained, such a method basically decomposes intothree steps: First, a microfludic surface processing device 10 a-10 hsuch as described above is provided, with the processing structure 21,21 a facing the surface 40 to be processed (or somehow orientedconveniently with respect to the surface 40 to enable surfaceprocessing/patterning); Second, a processing liquid 15 is dispensed viathe outlet aperture 11, whereby the processing structure 21, 21 aintercepts a flowpath of the processing liquid 15 dispensed; and third,particles/molecular species 151, 153, 155 in the liquid 15 can betransferred to the surface 40 via the processing structure 21, 21 a, bybringing the latter in (and out of) contact with the surface 40.

In reference to FIG. 14 (and also to FIGS. 5-6), a well defined volumeof processing liquid 15 is provided by the MFP head 16. The probe tip 21(and also partly the cantilever 22) of an AFM probe 20 intersects theresulting liquid 15 envelope. The probe tip 21 is therefore continuously“inked” with chemicals contained in the liquid 15. The chemicals diffuse(creep) along the probe tip 21 of the AFM probe 20 towards the apex andare deposited onto the substrate. Proper surface functionalization ofthe probe tip 21 can be needed to ensure efficient transport of thechemicals to the apex of the tip.

In addition, the method can further include providing an immersionliquid 50 between the face 17 and the surface 40, as depicted in FIG.15. The processing liquid 15 is thus dispensed within the immersionliquid 50, and preferably forms a laminar flow of processing liquid 15confined in the immersion liquid 50. Chemicals 151 remain confined inthe small volume of processing liquid 15 dispensed by the MFP head 16.The probe tip 21 is therefore continuously “inked” with chemicalscontained in the liquid 15, which chemicals otherwise remain in theprocessing liquid 15. Careful choice of processing liquid 15 vs.immersion liquid is therefore preferred. A number of combinations can becontemplated where the molecules chosen “like” to creep on the probe tip21 material and do not detach from the probe tip 21 material as soon asthey face the immersion liquid environment. Again, the chemicals 151diffuse towards the apex of the probe tip 21 and are deposited onto thesubstrate, but with better control of the diffusion volume. A pattern155 is formed on the surface 40. Here too, a proper tip 21 surfacefunctionalization may be needed. Note that, in FIG. 15, the probe tip 21is not completely immersed within the confined liquid 15. The sharp endis only “inked” trough creeping of the molecules on the surface of theprobe tip 21, which provides high resolution. This is not the case inFIG. 14, where the probe tip 21 is completely surrounded by the confinedliquid 15.

In addition, a chemical reaction can be involved, which is locallycontrolled by bringing the probe tip 21 in and out of contact withsurface 40 of the substrate. The methodology discussed here is howevernot limited to chemical reactions. Material can also be transferred tothe substrate via specific surface interactions, such as Van der Waals,hydrogen bonds and/or steric interactions.

In the example of FIG. 18, the AFM tip 20 is completely surrounded bythe processing liquid 15. A chemical reaction takes place at the surface40 due to an activation energy provided by the AFM tip 20 (for exampleby way of an electrical, mechanical or a thermal stimulus). Therefore,methods of surface processing can further include energizing theprocessing structure 21, preferably thermally or electrically, to enablea chemical reaction to take place at the surface 40. In variants, acatalytic action of the probe tip 21, properly prepared, e.g. platinum,enzymes, can serve this purpose.

Referring now to FIGS. 16, 17 and 19: the step of particle transfer cannotably include generating a lipid bilayer (or the like) 154 at thesurface 40 of the processing structure 21, 21 a, i.e., the surface ofthe probe tip 21 (FIGS. 16-17), or the surface of a rounded processingstructure 21 a (FIG. 19). As illustrated in FIGS. 16-17, amphiphilicmolecules 151 can be provided by the processing liquid 15. In theimmersion liquid 50, the lipid bilayer 154 forms, surrounding the probetip 21. Such lipid bilayers 154 function like a conveyor belt because ofthe high mobility of the amphiphilic molecules in the lipid bilayer 154.Lipid strands can therefore be patterned 161 on the substrate surface40, by bringing the probe tip 21 into contact therewith, wherebyhydrophilic end groups interact with the surface 40.

Next, the method can further include transporting molecular species 153via a lipid bilayer 154 formed on the probe tip 21 to transfer themolecular species 153 to the surface 40, as illustrated in FIG. 17. Herethe conveyor belt is used to transport the molecular species 153, whichare integrated into the lipid bilayer 154 from the flow confinement ofthe MFP head 16. The molecular species 153 are transferred to thesubstrate at the apex of the probe tip 21 via specific surfaceinteractions, e.g. cell membrane receptor binding, to form specificpatterns 163 thereon.

In the example of FIG. 19, use is made of a protruding feature 21 a(e.g. a rounded tip/bump), which is coated with a mobile layer ofreagent. This could for instance be a lipid double layer (as in FIG. 16or 17), including membrane proteins 153 to scan for receptors on cells.

The above embodiments have been described in reference to theaccompanying drawings and may accommodate a number of variants. Inembodiments, several combinations of the above features (as recited inrespect of one or the other aspect of the invention) may becontemplated. Detailed examples are given next.

Preferred embodiments basically make use of a multilayered MFP 16 b andan AFM-like cantilever.

As in microfluidic devices in general, the present surface processingdevices can be equipped with user chip interfaces and closed flow paths.Closed flow paths facilitate the integration of functional elements(e.g. heaters, mixers, pumps, UV detector, valves, etc.), which can beintegrated to present surface processing devices, while minimizingproblems related to leaks and evaporation.

An example of MFP head 16 component is depicted in FIG. 1 or 3. This MFPhead 16 is preferably fabricated as a multilayer device, to ease thefabrication of inner microchannels 11 c, 12 c (as visible in FIG. 3).Such MFP heads 16 can be microfabricated using Silicon (Si) wafers,although other materials can be used. For example, an upper layer (Si),i.e., a Si lid can be provided on top of a HFC chip. A single-side and adouble-side polished Si wafer can be used for the Si and HFC chip,respectively. Both wafers are e.g. 4 inch in diameter and 400 μm inthickness (Siltronix, Geneva, Switzerland). The microstructures can bemade using standard photolithography, photoplotted polymer masks(Zitzmann GmbH, Eching, Germany) and DRIE, see e.g. STS ICP, SurfaceTechnology Systems, Newport, UK. The microchannels of the HFC chips canbe etched 50 μm deep into the upper face of the HFC wafer. The bottomside of the wafer can be processed to form mesas and posts, ifnecessary, to a height of 50 μm. Opening the apertures can be performedusing DRIE etching from the bottom side of the HFC wafer. Well definedapertures with lateral dimensions of less than 10 μm can thereby beobtained. The apertures can be more accurately fabricated when a thin Siwafer is used for the HFC chip while the lid wafer can remain thick toprovide mechanical strength to the MFP head 16.

The Si lid can be produced by etching vias with a diameter of 800 μmtrough a one side polished wafer. Next, assembly of both wafers isachieved by spin coating ˜3 μm of a polyimide adhesive (HD MicrosystemsGmbH, Neu-Isenburg, Germany) onto the polished side of the lid wafer andby subsequently aligning and bonding both wafers. Bonding can take placeat 320° C. with 2 bar pressure for 10 minutes (PRESSYS LE, Paul-OttoWeber GmbH, Remshalden, Germany). The upper lid can be terminated withany appropriate layer for enabling sensing, if necessary. The MFP heads16 can then be diced and stored. Mounting the ports can be carried outusing epoxy adhesive rings (Nanoport™ Assemblies from UpchurchScientific, Ercatech, Bern, Switzerland, epoxy adhesive rings aresupplied). The use of standard ports and fittings in place of e.g.molded block of PDMS diminishes labor needed for assembling a MFP head16. MFP heads 16 are preferably tested for leakage and clogging beforeactually mounting the ports, as incursion of adhesive into themicrochannels cannot be excluded. In that respect, a disposable pipettetip can be cut to match the size of the vias and liquid can be pushedthrough the channels while observing with a magnifying glass if dropletsare able to exit the apertures without leaking elsewhere. Alignment ofthe ports with the vias can finally be done manually. A subsequentbonding takes place, e.g. at 140° C. for ˜1 hour on a hotplate or in anoven.

MFP heads 16 such as discussed above are particularly useful notably forsurface processing applications. Surface processing applications, unlikebiological applications, deal with potentially smaller patterns and abroader range of liquids and chemicals. Employing a thin Si wafer (e.g.100 μm in thickness) to fabricate the HFC chip, one can fabricate welldefined apertures with lateral dimensions of less than 10 μm, usingconventional DRIE or focused ion beam. The mechanical strength of theMFP head 16 is merely provided by the Si lid.

Incidentally, multilayered heads such as discussed above are also moreamenable to using many processing liquids because apertures can be smalland close to each other with horizontal microchannels sufficientlyfanning out for leaving sufficient space for adding many ports on the Silid. Embodiments of the invention therefore extend to multipleprocessing liquids 15, used in conjunction with one or more processingstructures 21 (with possible several processing structures per flow orone or more processing structures per liquid flow).

Concerning now the AFM components, accurate positioning of microfludicsurface processing devices 10 a-10 h as contemplated herein can beachieved by means of any appropriate positioning systems, as usuallyused together with MFPs or SPM. Using SPM-like positioning systems, theposition of the added tip with respect to the surface can therefore becontrolled with improved accuracy (e.g., to within about 0.1 nm) bymoving either the sample or the mircrofludic surface processing device10 a-10 h.

The added tip is preferably very sharp; on the nanoscale order. For someapplications, metallic tips can be used, and are typically made ofplatinum/iridium or gold. The cantilever 22 is otherwise typically madeof silicon or silicon nitride with a probe tip 21 radius of curvature onthe order of nanometers. More generally, silicon probe tips 21 astypically used for non-conductive AFM measurements are preferred, whichcan be obtained e.g., by isotropically etching a silicon pillarstructure until the required sharpness is reached.

The AFM-like cantilever can be fixed to, mounted integral with or stillglued to a lower side of the MFP head 16. In FIG. 1, the cantilever issimply glued at one end point 23 to the processing side 17 of the MFPhead 16.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes can be made and equivalents can be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications can be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims. In that respect, not all the components/steps depicted in theaccompanying drawings need be involved, depending on the chosenembodiments. In addition, many other variants than explicitly touchedabove can be contemplated. For example, typical SPM accessories can beused, such as coarse and fine positioning systems for bringing theprocessing feature in contact with the processed surface 40. Finally,beyond applications mentioned above, the person skilled in the art mayrealize that the present invention may find other applications in thefollowing technical fields:

-   -   electrodeposition of metal for direct writing of interconnects        and mask repair;    -   biopatterning;    -   living cell stimulation and sensing;    -   screening of biological libraries (sensing of binding        interactions);    -   multiplexed local chemistry;    -   multiplexed chemical contrast imaging;    -   chemically induced lithography, e.g. proton delivery for        triggering decomposition reactions in chemical resists; and        local activation of cross-linking reactions by providing        catalytic reagents.

What is claimed is:
 1. A microfluidic surface processing device,comprising: a microfluidic probe head having, on a face, at least oneaperture, including at least an outlet aperture; and a processingstructure extending outward and perpendicular with respect to the face,the processing structure being dimensioned and located with respect tothe outlet aperture such that it can intercept a flowpath of liquiddispensed via the outlet aperture.
 2. The microfluidic surfaceprocessing device according to claim 1, wherein the microfluidic probehead includes at least an inlet aperture on the face, comprising: theoutlet aperture and the inlet aperture are dimensioned and positionedsuch as to allow for collecting, via the inlet aperture, liquiddispensed via the outlet aperture; and the processing structure isdimensioned and located with respect to the inlet aperture and theoutlet aperture to intercept the flowpath of liquid dispensed via theoutlet aperture and collected via the inlet aperture.
 3. Themicrofluidic surface processing device according to claim 2, comprising:an electrical circuit configured to measure an electrical response, suchas an electrical conductivity, an electrical capacitance, or anelectrochemical potential, of liquid collected via the inlet aperture;and feedback control means coupled to the electrical circuit, configuredto control a rate of processing liquid dispensed via the outlet aperturebased on an electrical response measured via the electrical circuit. 4.The microfluidic surface processing device according to claim 1,wherein: an average diameter of the outlet aperture at the level of theface is between 0.5 and 1000 micrometers; a distance between theprocessing structure and the outlet aperture is between 5 and 2000micrometers; and a distance between the outlet aperture and a inletaperture of the microfluidic probe head, if any, is between 5 and 2000micrometers.
 5. The microfluidic surface processing device according toclaim 1, wherein the microfludic surface processing device includes acantilever mechanically connected to the microfludic probe head, and theprocessing structure is a probe tip terminating the cantilever.
 6. Themicrofluidic surface processing device according to claim 5, wherein thecantilever is a scanning probe microscope cantilever, and the cantileveris anchored to the microfluidic probe head.
 7. The microfluidic surfaceprocessing device according to claim 6, wherein the cantilever is fixedvia a fixed portion at the face, the fixed portion, distant from theprobe tip, and the cantilever further include a free portion, extendingopposite to the probe tip with respect to a main axis of the cantileverand configured to seal one of the apertures when urged against it. 8.The microfluidic surface processing device according to claim 7, whereinthe fixed portion is opposite to the probe tip with respect to the freeportion or the free portion is opposite to the probe tip with respect tothe fixed portion.